Technical Abstract:
Biochar, generated by pyrolysis (i.e., heating biomass under low-oxygen conditions), results in incomplete combustion, producing a fine, grainy, highly porous material, 200 – 1,000 um in diameter. Benefits of biochar production include generation of bio-fuels, useful soil amendments for fertilizing crops and binding heavy metals, sequestering biocarbon, and reducing environmental gas emissions. Data also suggest that biochar-amended soil improves the phyto-beneficial microflora and depresses populations of human pathogens within the family Proteobacteria (Salmonella, etc.).
The influence of biochar on the survival of E. coli O157:H7 (EHEC) in crop soil was determined.
Twelve types of biochar (slow pyrolysis or fast pyrolysis type) were generated in on-site reactors. A three-strain composite of EHEC (6 log CFU/g, final population) was added to autoclaved crop soil + 10% (final concentration) of one of 12 types of biochar. Samples were adjusted to a final moisture content of 17.6% and stored in sealed bags at 22 deg C. Populations of EHEC were determined weekly up to five weeks.
Fast pyrolysis-produced switchgrass (FP-SG) and FP horse litter (FP-HL) biochars inactivated 3.52 and 2.58 log CFU/g more EHEC than did control soil by day 14. By day 28, FP-SG, FP-HL, and FPpelleted-SG biochars all reduced EHEC to undetectable levels (less than 1.2 log CFU/g) by direct plating versus control soil, which contained 5.45 log CFU/g of EHEC on day 28. FP oak biochar inactivated 3.1 log more EHEC than control soil on day 28, and at day 35, no EHEC was detected in FP-oak soil by direct plating. Four slow pyrolysis biochars all inactivated 2 log CFU/g more EHEC than the control soil by day 28, including SG (1h at 500 deg C), mixed hardwood pellets (MHP, 1h at 500 deg C), and MHP (30 min at 700 deg C).
These results are the first to suggest that biochar amendments enhance the inactivation of E. coli O157:H7 in crop soil.